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Abstract

Indeed, I have come so far from when I first approached him in the summer of 2012. For all that, and much more, I am truly grateful.Jeff Seewald is another person with whom I have worked very closely with through the course of this thesis. I have thoroughly enjoyed my time in his lab. Jeff spent a lot of time teaching me how to set up high-temperature, high-pressure experiments and very patiently coached me the optimized techniques and systems for sampling. In addition, he has been 'a fountain of optimism' through long hours in the lab.I would also like to thank the other members of my thesis committee: Stefan Sievert and Shuhei Ono. Stefan played an instrumental role in getting me on the 9°50'N East Pacific Rise cruise in 2017, and provided insights into the microbial dynamics at Crab Spa (yes, it is spelled correctly this time). Shuhei was always enthusiastic to hear about my thesis progress, and offered valuable advice and encouragements during our meetings. I am also indebted to Frieder Klein who not only chaired both my thesis proposal and defense, but also went above and beyond, providing suggestions to this final draft.This thesis would not have come to fruition without the expert technical assistance of Sean Sylva, whose incredible patience and recommendations helped troubleshoot both the bomb setup and instruments used for my work in the Seewald Lab. Labmates from the first summer when I first started my experiments, Niya Grozeva and Justin Snook, both provided tremendous assistance, shared neatly-kept notes, and most importantly, offered lab companionship. I am also thankful to Zoe Sandwith, who kept the IRMS in the Wankel Lab humming, dealt with leaks in the Valco valve, did the argon sniffing, and took care many other issues that would have taken much longer to fix without her help.I have benefited greatly from the body of works carried out by many colleagues. Archived samples from the Seewald Lab, which were the main part of Chapter 3, were collected during numerous cruises before I entered the Joint Program. Many of these were collected with the help of Eoghan Reeves and Jill McDermott, both former advisees of Jeff's. They have been very generous in providing sample data and insights that were instrumental to my work. Annie Bourbonnais, Marv Lilley, and Dave Butterfield generously shared their Juan de Fuca Ridge sample data, which also made up a sizeable part of the compilation. Tina Lin and Mike Rappe provided crustal fluid samples, which became great complements to the Juan de Fuca discussions. Jesse McNichol's thesis work on Crab Spa incubations laid the groundwork for development of Chapter 4 of this thesis.The world-class education I had received for my PhD would not happened without the highly acclaimed field experts at WHOI and MIT. Moreover, the Academic Programs Office had been a propelling force behind the scene. I would like to specifically thank Meg Tivey, Jim Yoder, Julia Westwater, Lea Fraser, and Christine Charette. I am also indebted to John Farrington who, despite not being the Dean...